This invention concerns itself with electrical commutators and, more particuarly, concerns a design in which the commutating surface is arranged around the interior of a commutator.
As is well known to those skilled in this art, it has long been common practice to mold commutators in a cylindrical shape with the contacting surface on the exterior. This arrangement, of course, has proven to be a highly successful one for most applications and will undoubtedly remain as the standard for most applications.
The fabrication of commutators by means of a molding process has provided a relatively efficient and economical way of producing commutators which are highly reliable in use. This is particularly true with small commutators where the centrifugal forces experienced by the conductor segments are not large enough to cause the commutator to break apart during use. As commutator size increases, however, the tendency towards centrifugal disassembly increases, thereby imposing a practical upper limit on the size in which molded commutators may be fabricated.
My invention provides an arrangement of commutator parts in which the above described size limitations can be overcome. Briefly described, my invention employs an inverted commutator design in which the conductor segments are arranged around the interior of the commutator, rather than its exterior. A suitable matrix is molded between and around a plurality of segments arranged in a ring with their inner-facing brush contact surfaces defining an overall cylindrical shape. In one embodiment, the commutator is fitted with an outer casing for reinforcement against centrifugal disassembly during use. In an alternate embodiment, this reinforcement is provided by reinforcement bands embedded within the matrix during the matrix molding process. In this alternate embodiment, a connection ring is also embedded in the matrix as a convenient means for attachment of the commutator to a spider, and ultimately, a shaft.
The method of making a commutator by this invention involves the steps of arranging a plurality of conductor segments in a ring with their inner-facing contact brush surfaces defining a cylindrical shape. Then a matrix is molded around and between the segments. In my preferred method, this molding step is carried out within an outer reinforcement casing. In an alternate method, reinforcement bands are molded into the matrix so that they become embedded therein outside the ring of the conductor segments.
It is therefore an object of this invention to provide an inverted commutator in which the contact surfaces of the conductor segments are arranged around the inside of the commutator.
It is also an object of this invention to provide a commutator of the type described which can be economically produced with existing technology.
It is a further object of this invention to provide a commutator of the type described having sufficient strength for use in applications requiring extremely large diameters.
These and other objects of the invention will be more completely understood by reference to the accompanying drawings and the description which follows.